The solutions of mathematical models for the estimation of the kinetic, and biokinetic parameters of naphthalene, anthracene and pyrene during degradation in surface and subsurface soils are presented in this work. The models were developed using the twin concepts of rate-determining step and steady-state
approximation method. They described the biodegradation of single and a mixture of polycyclic aromatic hydrocarbons. Prediction of the concentration of the reactive PAHs with time was aided by fitting the models to the experimental data obtained from a soil microcosm reactor. Given an initial concentration of 100mg/L, approximately 2.9%, 1.9% and 1.4% of naphthalene, pyrene and anthracene present in the microcosm reactor at zero time were found to be utilized in a minute when the velocity of the reaction remained constant for the period.The rate-determining step model gave a better fit as its reaction rate constant (k) closely fitted the experimental values. Prediction by the steady state approximation model was not feasible as a comparative analysis of both single and multisubstrate results showed that the steady state approximation overestimates the biodegradation rates.Using the relative error method, results indicated that the rate-determining step model showed a deviation of 7.5%. The rate-determining step model was chosen because the differences in the model fits were small and its prediction of mixture experiment was more enhanced.